Is the Ozone Layer Recovering?

1. Is the Ozone Layer Recovering? Dr. Paul A. Newman http://code613-3.gsfc.nasa.gov/People/Newman/ NASA’s Goddard Space Flight Center Global Climate Change Forum The Field Museum, Chicago, Ill. March 25, 2006

2. Outline • Introduction • What’s the problem? • Some basic facts about ozone • What are the gases that cause ozone loss? • How does the ozone hole form? • What do the latest ozone trends look like? • Predictions - Where’s ozone headed? • Summary

3. Science begins with quality measurements (numbers) Aurora over Halley Bay Station, Antarctica, 75.6ºS 26.5ºE Brunt Ice Shelf, Coats Land 105 days of continuous darkness, twice per year re-supply Population: 65 in summer, 15 in winter

4. Farman, Gardiner, & Shanklin (1985) Farman et al. (Nature, 1985)

5. What is ozone?

6. Ozone Basic Facts O3 = Ozone is composed of 3 oxygen atoms. O3 inhalation becomes a problem at concentrations greater than 80 parts per billion sustained during a continuous 8-hour period (EPA). O3 absorbs harmful solar ultraviolet radiation. A necessary condition for life. O3 is mainly found in the the stratosphere. O3 both heats the stratosphere by absorbing UV and is a greenhouse gas (absorbing and emmiting in the Infrared). O3 concentrations are small (peak concentrations are about 10 parts per million at an altitude of about 32 km (20 miles). Mass: (Billion Metric Tons) Sun 1,9900,000,000,000,000,000 Earth 5,980,000,000,000 Global atmosphere 5,300,000 Global ozone 3

7. Atmospheric Structure Ozone Oxygen 100 60 Thermosphere 80 50 40 Mesosphere 60 Altitude (miles) 30 Altitude (km) 40 20 20 10 Troposphere 0 0 0 2 4 6 8 Ozone (parts per million)

8. Ozone Facts 100 60 Thermosphere 80 50 40 Mesosphere 60 Altitude (miles) 30 Altitude (km) 40 90% of ozone is in the stratosphere 20 20 10 10% of ozone is in the troposphere Troposphere 0 0 0 2 4 6 8 Ozone (parts per million)

9. What does ozone do?

10. Ozone Facts Ozone is the Earth’s natural sunscreen 100 60 Thermosphere 80 50 UVc - 100% Absorption Mesosphere UVb - 90% Absorption 40 UVa - 50% Absorption & Scattering 60 Altitude (miles) 30 Altitude (km) 40 20 20 10 Troposphere 0 0 0 2 4 6 8 Ozone (parts per million)

11. Health Facts • UV plusses: produces vitamin D in the skin - necessary to maintain levels of calcium and phosphorus (~10-15 minutes twice a week) • UV minuses: • Eye damage: cataracts, photokerititus (snowblinding), ocular cancers • Skin cancers: basal, squamous, melanoma • photoaging • Damage to various land species • Damage to aquatic species • Increased pollution levels in urban environments • Tropospheric ozone is a pollutant: aggravates asthma, reduces lung capacity, and increases susceptibility to respiratory illnesses like pneumonia and bronchitis Cataract Melanoma Mexico City

12. Future cancer rate projections Cases in excess of 1980 levels (~ 2000 per million) Without the protocol, excess cases would have increase unchecked

13. What chemicals cause ozone loss?

14. Source Chemicals • Cl is much more abundant than Br • Br is about 50 times more effective at O3 destruction From Ozone FAQ - see http://www.unep.org/ozone/faq.shtml

15. Atmospheric Chlorine Trends from NOAA/ERL - Climate Monitoring Division 102 years CFC-12 CFC-11 Steady growth of CFCs up to 1992 50 years CH3CCl3 CCl4 42 years 85 years CFC-113 5 years Updated Figure made by Dr. James Elkins from Trends of the Commonly Used Halons Below Published by Butler et al. [1998], All CFC-113 from Steve Montzka (flasks by GC/MS), and recent updates of all other gases from Geoff Dutton (in situ GC).

16. Global Stratospheric Chlorine trends Time evolution of chlorine From WMO (2003) - Figure 1-7

17. What causes the ozone hole?

18. How does chlorine get from our refrigerators to the Antarctic stratosphere? Cl catalytically destroys O3 Cl reacts with CH4 or NO2 to form non-reactive HCl or ClONO2 CFC-12 photolyzed in stratosphere by solar UV, releasing Cl Cl released by PSCs Carried into stratosphere in the tropics by slow rising circulation CFC-12 released in troposphere

19. Polar Stratospheric Clouds Central, Sweden January 14, 2003 - P. Newman

20. HCl PSC ClONO2 Cl2 HNO3 Antarctic ozone hole theory Solomon et al. (1986), Wofsy and McElroy (1986), and Crutzen and Arnold (1986) suggest reactions on cloud particle surfaces as mechanism for activating Chlorine Cl2 is easily photolyzed by UV & blue/green light HNO3 is sequestered on PSC

21. Polar Ozone Destruction 1. O3 + Cl ClO + O2 3. ClOOCl+h2 Cl+O2 3 O2 2 O3 2. 2 ClO + M ClOOCl + M Only visible light (blue/green) needed for photolyzing ClOOCl No oxygen atoms required Net: 2O3 + solar photon 3O2

22. 230 230 220 220 210 210 200 200 190 190 230 180 180 230 220 220 210 210 200 190 200 180 150 150 150 150 190 100 100 100 100 180 50 50 50 50 0 0 0 0 Ozone Hole timeline May Jun Jul Aug Sep Oct Nov Temp  Polar night falls and temp cool Sunlight induces catalytic O3 loss PSCs begin to form Chlorine is freed into reactive forms T become too warm for PSCs, O3 loss stops  Ozone hole breaks-up, mixes low ozone across SH  Ozone Cold T  PSCs + high Cly  het reactions  Large catalytic loss

23. What’s the latest on ozone trends?

24. October Antarctic Ozone

25. October Average Ozone Hole Low Ozone High Ozone

26. Arctic & Antarctic Trends • Substantial losses have occurred in the Arctic • Arctic levels are naturally higher because of the structure of the NH

27. Newchurch et al. (2003) • 35-45 km, 30-50˚N ozone • Note that the later year (post 1997) are above the downward slope • Ozone is no longer decreasing (1st step in the recovery process)

28. Where’s the ozone hole headed?

29. Model size estimates

30. Ozone Hole Area

31. Increases in long-lived gases 3 Halocarbons (e.g., CFCs) 2 N2O (nitrous oxide) CH4 (methane) Warming 1 Tropospheric ozone increase Human produced Radiative Forcing (Watts/m2) CO2 0 Stratospheric ozone depletion -1 Cooling Ozone changes -2 Ozone and climate change • Ozone change is not a primary cause of climate change. • Ozone depleting substances contribute to climate change. • Ozone changes causes a climate response that is generally larger than the Halocarbon response. • Climate change may seriously impact ozone levels. See “Climate Change 2001: The Scientific Basis”

32. Summary • Ozone is the critical gas for screening solar UV radiation. Quality, long-term observations are critical for assessing change! • Ozone loss resulted from human produced ozone destroying substances (ODS: CFCs and halons). These chemicals have extremely long lifetimes. • ODSs have been regulated under international agreements and are slowly decreasing. • Ozone levels are not getting worse, but we can’t say that things are getting better (yet). • The ozone hole will recover by about 2068. • Every year of delay in regulating ozone would have resulted in a 9 year delay of recovery. • The impact of climate change on ozone recovery is very uncertain at present.